Over one-third of the volume of in-the-body heart defibrillators is allocated to the capacitor, approximately 20 cm3. Intrinsic dielectric properties, demonstrated in integrated circuit technology, imply that this volume could be reduced to less than 1 cm3. Spire Corporation proposes to use metalorganic chemical vapor deposition (MOCVD) to form thin film ferroelectric ceramic in a capacitor structure with at least 100 times greater energy density than presently available commercially. Thin film dielectrics based on ferroelectric compounds have extremely high dielectric constant (over 1,000) and high electrical breakdown strength (100 V/microm) when deposited without voids or other field- enhancing defects. In Phase I, Spire demonstrated a single-layer capacitor with high energy density and the capability to uniformly deposit a dielectric with sufficient area as proof-of-principle that full-sized prototype capacitors can be built in Phase II. In Phase II research Spire proposes to optimize the dielectric composition for the temperature range In the body cavity containing the defibrillator, to optimize the capacitor design to fit into existing electronics, and to produce a sufficient number of prototypes that the defibrillator manufacturer can test this advanced component for compliance with regulations. Successful completion of the proposed program will lead to immediate introduction of smaller cardiac defibrillator devices with improved patient comfort A smaller defibrillator would have immediate impact on patient comfort The commercial market is assured because the capacitor's cost is a small fraction of the total value of a cardiac defibrillator system.